fix: remediate 10 review findings in communication spine

- Fix createSession race condition with in-flight promise map
- Fix listener leak: always cleanup previous subscription per client
- Fix REST timeout returning HTTP 200 — now rejects with 504
- Fix fire-and-forget Discord sends — await with error handling
- Fix non-null assertion on client.user in Discord plugin
- Fix TUI disconnect mid-stream deadlock (reset streaming state)
- Add connect_error handler to TUI and Discord plugin
- Add connected guard on TUI message submit
- Add relayEvent guard for disconnected sockets
- Sanitize error messages sent to WebSocket clients
- Add error logging/context to AgentService create/prompt/destroy

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/cli/src/tui/app.tsx

@@ -32,7 +32,20 @@ export function TuiApp({ gatewayUrl, conversationId: initialConversationId }: Tu
     socketRef.current = socket;
 
     socket.on('connect', () => setConnected(true));
-    socket.on('disconnect', () => setConnected(false));
+    socket.on('disconnect', () => {
+      setConnected(false);
+      setIsStreaming(false);
+      setCurrentStreamText('');
+    });
+    socket.on('connect_error', (err: Error) => {
+      setMessages((msgs) => [
+        ...msgs,
+        {
+          role: 'assistant',
+          content: `Connection failed: ${err.message}. Check that the gateway is running at ${gatewayUrl}.`,
+        },
+      ]);
+    });
 
     socket.on('message:ack', (data: { conversationId: string }) => {
       setConversationId(data.conversationId);
@@ -69,7 +82,14 @@ export function TuiApp({ gatewayUrl, conversationId: initialConversationId }: Tu
 
   const handleSubmit = useCallback(
     (value: string) => {
-      if (!value.trim() || isStreaming || !socketRef.current) return;
+      if (!value.trim() || isStreaming) return;
+      if (!socketRef.current?.connected) {
+        setMessages((msgs) => [
+          ...msgs,
+          { role: 'assistant', content: 'Not connected to gateway. Message not sent.' },
+        ]);
+        return;
+      }
 
       setMessages((msgs) => [...msgs, { role: 'user', content: value }]);
       setInput('');